Geoscience Reference
In-Depth Information
Figure 2.12 The rainforest is abundant with woody vines throughout the canopy.
Taken on S
ao Tom
e Island, Republic of S
ao Tom
e and Principe.
(Photo courtesy of Rob-
~
~
ert Drewes, Ph.D., California Academy of Sciences.)
the ancestors of the domesticated yams (Africa) and sweet potatoes (South Amer-
ica), store nutrients in roots and tubers.
Competition for sunlight by plants can be deadly. Some vines are considered
stranglers as they quite literally strangle the host tree. Strangler vines need sunlight
to grow and reproduce. Seeds falling to the ground quickly die in the deep shade
and infertile soil of the tropical rainforest. Stranglers begin life as epiphytes with
their seeds deposited on the branches of a host tree by birds and small animals that
have eaten their fruit. The seeds sprout and send long roots to the ground. The
roots rapidly increase in diameter and successfully compete for water and nutrients
in the soil. As the strangler matures, branches and leaves grow upward, creating a
canopy that blocks sunlight. In time the tendrils, now vine-like, fuse with each
other effectively surrounding and killing the host tree. Additionally, roots are
sent out and wrap around the roots of the host tree competing for nutrients (see the
sidebar on p. 35). Many stranglers are fig trees (Moraceae family); other genera of
stranglers include pitch apple (Clusiaceae), umbrella tree (Araliaceae), tree jasmine
(Rubiaceae), and Coussapos (Moraceae). Some do not kill their host tree.
Epiphytes.
Epiphytes (also called air plants) live on other plants. Typically, they
are not parasitic, although they do compete for resources. Epiphytes attach to
tree branches and use the soil and dust particles they trap within the canopy to
